WaveForms is a free to use spline / path editor for Phaser.

You can buy the complete source code to WaveForms:

The full source code to the WaveForms Path Editor
  • Easily Add and Remove points on the path
  • Toggle Grid Snapping
  • Keyboard Short-cuts for all functions
  • Edit 8 paths at once
  • Export as JSON data
  • For Phaser 2 / CE only
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$0 was $10

With the source you can run WaveForms locally and disable the splash screen. You're then free to add whatever additional features you'd like: tweak the export code, merge it into your own tools, adjust the grid or game size or whatever you require.